Pressure-compensated telephone unit



April 25, 1950 1 BERANEK PRESSURE COMPENSATED TELEPHONE UNIT 2 Sheets-Sheet l Filed March e, 1945` pril 25, 1950 L. L. BERANEK PRESSURE COMPENSATED TELEPHONE UNIT F'iled March 8, 1945 PRESSURE RESPONSE IN DECIBELS PRESSURE RESPONSE BM DECIBELS 2 Sheets-Sheet 2 O Sea Level Response l/`\ i9 LU l u D:

40,000 F t Response FREQUENCY IN CYCLES PER SECOND E svp' l; 40,000 FtResponse |00 |000 lQOOO FREQUENCY IN CYCLES PER SECOND @y 'Quay/WM d wel Patented Apr. 25, 1950 UNITED T E S PRESSURE-COMPENSATED TELEPHONE UNI Application March 8, 1945, Serial No. 581,689

6 Claims.

This invention relates to telephones and more especially to a compensated receiver or the like for use at high altitudes.

An object of the invention is to improve telephone receivers and to provide a device for producing sound at the ear from electrical audio frequency current alternations, whose output can be adjusted so as to become greater as a function of altitude, and at the same time preserving a flat response curve characteristic at various altitudes. It is also an object of the invention to provide a simple, eicient and reliable compensating mechanism for a receiver. Other objects will appear from the following description of the invention.

In the accompanying drawings:

Fig. l is a vertical diametrical section of the receiver of the invention;

Fig. 2 is a digrammatic view illustrating response curves of a conventional receiver; and

Fig. 3 is a diagrammatic view illustrating response curves of the receiver of the invention.

The normal response curve of a conventional receiver or headphone obtained by plotting frequency against sound pressure levels is a, relatively fiat curve of definite value, as illustrated by the curve denoted sea level response in Fig. 2. At higher altitudes, the response curve of the conventional receiver shows a drop in soundl pressure values and is characterized by a pronounced peak at higher frequency values, as may be observed from an inspection or the 40,000 ft. response curve in Fig. 2. Both of these changes appreciably lessen intelligibility.

The receiver of the invention maintains satisfactory sound pressure values at higher altitudes and substantially eliminates the high frequency peak. Fig. 3 illustrates its response curves at sea level and also at 40,000 ft. altitude.

Included in the improved receiver are means for moving the pole pieces and a covering toward the diaphragm, with such means being responsive to changing conditions resulting from variation in altitude and rareed air. The receiver also includes means for limiting decrease in volume of air between the diaphragm and the covering surrounding the pole pieces resulting from the pole pieces moving closer to the diaphragm.

Considering the receiver of the invention in greater detail, numeral l indicates a casing member formed with a rim i2 which is provided along its inner periphery with threads I4. A cap I5 is adapted to be detachably engaged within the rim I2 by a threaded annular portion I8.

The base of the casing Il] is recessed to receive contact elements 26 and 22, through which extend screws 24 and 26 as illustrated at the righthand side of Fig. 1. The contact elements 20 and 22 are preferably slotted in some convenient manner to permit the insertion of input terminals 28 and 30, the extremities of which are secured in place by means of the screws 24 and 26. The latter may be parts of binding posts or other external conventional circuit connections, not shown.

Secured in spaced relation to the base of the casing lil is a cylindrical shell 32 which has received therein a stationary sleeve member 3i in which is slidably supported a ring member 36. The sleeve 3s is supported at the right-hand edge, as viewed in Fig. 1, against an insulating disc 38 to which are secured the extremities of the terminals 28 and 3l). Numeral 40 denotes coils surrounding pole pieces 42 and 44 fixed in relation to the ring 36. Located in axially spaced relation to the polar extremities of the pole pieces is a diaphragm 54 held against the inner left-hand edge of the sleeve 34, as viewed in Fig.

1. Numeral 55 indicates a protecting cap of rub v bei-ized cloth or other suitable material for excluding moisture from the diaphragm. and 62 denote flexible connecting wires extending between the terminals 28 and 30 respectively and the ends of the coils.

passes through the coils 40.

The ring 3B, together with the coils and pole pieces, is adjustably secured to the sleeve 34 by means of a circular flexible covering 4B which flange, as by means of an adhesive and is similarly attached to edges of the ring 36. As the latter ring is arranged in spaced relation to the l ange 50, there is left an intermediate portion of the covering which is unattached. This unattached portions functions somewhat like a hinge allowing the ring 3o to move in and out of they sleeve 34.

The ring 3S, pole pieces l2-44, covering 4B, and I coils 4t are normally held as a stationary magnetic unit in spaced apart position relative to the diaphragm 5t by means of a spring washer 458'y which is interposed between the flange 50 and a shouldered portion of the ring 36.

35 may come to rest against the insulating disc 38.

The diaphragm vibrates, producing sound, when an alternating currentv If advancedl to an extreme position toward the right, the ring However, in a normal operating position, the ring member is spaced from the disc 38, and is arcane By reason of this construction, this member 65 is-'fy sensitive to outside pressure iiuctuations.- The aneroid device is coaxial with the diaphragm and casing, and is loosely supported at some convenient point as in back of the insulating disc 38, and the plunger portion isallowe'd to project through an opening l in the disc 38 and toi engage against a thin disk or plate member 64 atY the back of the coil and pole-pieces. assembly. The cylindrical portion E8 of the aneroid 65 is held against the disc 64 with a light pressure by" means of an adjustment screw 12 which is recessedin"- an external openingllform'ed in the' base of the casing l0, and bears at its 'inner end against a wear platey set across-'theA closed rear end ofthe' aneroid member. This aneroid member. then' becomesy the means resiliently urging theringgmemberv 36 toward 'the left.

The aneroid member when properly adjusted maintains the pole pieces and covering 46 against the spring washer 48 in a position such that the polar faces of the pole pieces lie'fin a suitably spaced'relation with respect to the diaphragm 54, to4 provide' a` nat response curve'at sea: level. In additiomthe aneroid member is responsive to changing pressure conditions encountered at higher altitudes. pressure at .such higher altitudes, air sealed within the aneroid expands and advances the plunger S8. against the'disc' which forces the .ring memberr 36 against the spring 43 into aposition in whichthe pole pieces are-brought more closely adjacent Vto the diaphragm. This automatically compensates for rarefied air and lower sound pressure levels.. 'By selecting a suitable distance through which the plunger moves during a known range ofy altitude values, there is obtained ameans .l

of providing asatisfactory. response 'curve which compensates 'for variance-.in sound' pressure levelsl at highaltitudes.' GoodV results have` been obv'- taine'd usingY a spacing or travel distance for the pole pieces of from .01v inch to .031 inch.

A screen piece-4l is provided in thercovering 45 and-back plate 4l which-permits impeded passage ofair from the space between .thedi'aphragm and the back plateinto theregion enclosed by ring 36 and. also reverse movement, of` the air. screen. piece permitsv limited movement of air fromthe, space.y immediately behind .the diaphragm to the space at-36, andthe limpedance of air by the screenandthe small size ofthe clearway throughy the coveringV and backplate M' is necessary for'the obtaining of auniformresponse characteristic. At higher altitudes, the air in the space between the diaphragm and the covering 4%" becomes rareed" and much more. compressible,. resulting in a condition where the air' With decrease in. atmospheric This becomes more pronounced, especially at high frequencies. Such decrease must be limited in degree, however, or an ideal response characteristic will not be obtained.

I have designed the covering 46 and back plate di tov provide. for a limited'decrease.` in--volume of thelspace between vthe diaphragm and covering as the pole pieces move closer. It will be noted that the flange 50 is characterized by an appreciable radial-width, and as a result, when the covering 46 is attached to it, there occurs a substantial reduction in area of that portion of the covering-which iss-free to move. The reduction inA area-isso chosen' that, having regard to the actual extent of. movement of the covering, there will always be preserved a suiiiciently large volume of,A air-forrth'e screen piece 4l to function in a satisfactory manner. The result of this is to smooth out the frequency peak and provide 'for high intelligibility at all altitudes.

The numberof v'turns/of' the 'screw'l required for 'agiven adjustmentmay be=used asa Calibra.'-

tion of the spacing of the pole-pieces fromtheY diaphragm. Also, othery types-1' of air. chamber controls and other devices mayfberesorted to.' Similarly, theoovering means" may be modified in various ways to provide a limit'on decrease of volume.V

lt willbe 'se'enl that the invention provides.

means for maintaining uniform performance of a headphoneatvarying altitudes, thus protecting'-Y intelligibility ofk speechrand eliminating dii-=v culties arising-athigher frequencies. Thel desY vice may/or may'notbe self-regulatory, according to the requirements which the u-nit`v is put to. The construction-described as'V aV preferred rernhodiment of the invention is-simpIe, cheap, and

readily carried out with current forms ofreceiver' assembly.

While i-n have-shown a preferred embodiment.

of my invention, itshould be'underst'ood that various changes and modi'cations maybe resorted to, in keeping with the spirit of the in'- vention as defined by the appendedclaims.

Having thus described my invention, what` I;

claim is:

l; A headphone for use at varying altitudes.

comprising'- a' casing, an air-impervious diaphragm receivedinthe f casing, pole pieces ar ranged in spaced'relationto the diaphragm, coils surrounding the pole pieces, a flexible aircon-v iiningv covering member surrounding the pole pieces and means-connecting said covering inem@v ber and diaphragm to form therebetween an air containing space co-extensivewith the major area of the diaphragm, altitude-responsive means for causing relative movement of-'theY pole piecesl cured in the casing,-polepieces arranged in spaced4 relation to the diaphragm, coils surrounding! thev polev pieces, ring means for supporting thev pole pieces and coils, said ring means'being sl'idably received inthe -casingya covering member secured vto the coils and pole pieces, said covering extending into overlapping relation with a flangeon the said casing and xed thereto, spring means interposed betweeny the flange and the ,ringV member adapted to maintain the pole pieces iir spaced relation tothe diaphragm, and means responsive to a decrease in atmospheric pressure for resiliently urging the pole pieces toward the diaphragm against the said spring means.

3. A headphone compensated for use at varying altitudes comprising a casing, a diaphragm secured in the casing, pole pieces arranged in spaced relation to the diaphragm, coils surrounding the pole pieces, ring means for supporting the pole pieces and coils, said ring means being slidably received in the casing, a covering member secured to the coils and pole pieces, said covering extending into overlapping relation with a ange on the said casing and fixed thereto, spring means interposed between the ange and the ring member adapted to maintain the pole pieces in spaced relation to the diaphragm, means responsive to atmospheric pressure change for resiliently urging the pole pieces toward the diaphragm against the said spring means, and an adjustment means for regulating the spacing of I the pole pieces and diaphragm.

4. An earphone comprising an earpiece having a diaphragm closely adjacent a face thereof; and means for moving the diaphragm consisting of the following parts, which parts are located further from said face than is said diaphragm; electromagnetic means for vibrating said diaphragm, and means responsive to changes in atmospheric pressure for bodily moving said electromagnetic means toward said diaphragm in response to decrease in atmospheric pressure and away from said diaphragm in response to an increase in atmospheric pressure.

5. The device of claim 4 wherein the lastnamed means at least partially supports said electromagnetic means.

6. A pressure compensated telephone unit having opposed spaced electrical reactance elements, at least one being a diaphragm capable of vibration relative to the other at voice frequencies, and being constructed to form a closed chamber therebetween, a limited vent in communication with the said chamber, a resilient support for the other said reactance element adjacent the diaphragm, and an expansible and contractible barometric device on said support having a fixed base, and oppositely in hearing with said other reactance element in a relation to move the same in response to change in ambient air pressure against the action of said resilient support to vary the spacing of the reactance elements inversely as the pressure varies.

LEO L. BERANEK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 977,981 Stuart Dec. 6, 1910 1,414,105 Timmons Apr. 25, 1922 1,602,696 Midgley Oct. 12, 1926 1,743,453 Hillhouse Jan. 14, 1940 2,364,485 Spencer Dec, 5, 1944 

